Physiology LC10 Mechanics of Respiration PDF

2. elevation and depression of the ribs to increase and OUTLINE decrease the anteroposterior diameter of the chest...

2. elevation and depression of the ribs to increase and OUTLINE decrease the anteroposterior diameter of the chest cavity I. RESPIRATORY SYSTEM A. Movement of the diaphragm II. MUSCLES OF VENTILATION Normal Breathing A. Movement of the diaphragm - Inspiration: contraction of the diaphragm pulls B. Movement of the Rib Cage the lower surfaces of the lungs downward III. AIR MOVEMENT AND PRESSURE CHANGES IN THE LUNGS - Expiration the diaphragm simply relaxes, and A. Pleural Pressure the elastic recoil of the lungs, chest wall, and B. Alveolar Pressure abdominal structures compresses the lungs C. Transpulmonary Pressure and expels the air. D. Lung Compliance Heavy Breathing E. Surfactant and Surface Tension - Elastic forces not sufficient for rapid expiration F. Effect of the Thoracic Cage on Lung Extensibility - Abdominal muscles contract to exhale more G. Work of Breathing rapidly IV. PULMONARY VOLUMES AND CAPACITIES A. Pulmonary Volumes B. Movement of the rib cage B. Pulmonary Capacities Increase 20% of AP diameter during maximum inhalation C. Minute Respiratory Volume Muscles of inspiration: V. ALVEOLAR VENTILATION - External Intercostals A. Anatomic vs Physiologic Dead Space - Sternocleidomastoid muscles - lift upward on B. Rate of Alveolar Ventilation the sternum VI. FUNCTIONS OF THE RESPIRATORY PASSAGES - Anterior serrati - lift many of the ribs A. Trachea, Bronchia, And Bronchioles - Scaleni - lift the first two ribs B. Mucus Lining of the Respiratory Passageways, and Muscles of expiration: Action of Cilia to Clear the Passageways - Abdominal recti C. Cough Reflex - Internal intercostals D. Sneeze Reflex - Lung floats in the thoracic cavity E. Normal Respiratory Functions of the Nose - Well lubricated by the pleural fluid F. Vocalization - Continuous suction of excess fluid into lymphatic channels - slight suction between the visceral surface of the lung pleura and the I. RESPIRATORY SYSTEM parietal pleural surface of the thoracic cavity (pleural pressure) Primary Goal: provide oxygen and remove carbon dioxide: gas exchange 4 major functions: III. AIR MOVEMENT AND PRESSURE CHANGES OF THE LUNGS 1. Pulmonary ventilation 2. Diffusion of oxygen and carbon dioxide between alveoli A. Pleural Pressure and blood - It is the pressure of the fluid in the thin space between 3. Transport of oxygen and carbon dioxide the lung pleura and chest wall pleura 4. Regulation of respiration - At the beginning of respiration = -5 cm of water– hold lungs open during rest - During inspiration increases to – 7.5 cm of water – outward pull of the chest wall B. Alveolar Pressure - The pressure of the air inside the lung alveoli - If glottis opens and no airflow- equal pressure throughout the respiratory tree = atmospheric pressure - zero reference pressure (0 cm of water) - Zero reference: in equilibrium with the atmosphere - During inspiration - alveolar pressure falls to -1cm of water – this slight negative pressure would be enough to pull 0.5 L of air into lungs in 2 sec (quiet respiration) - During expiration – alveolar pressure rises to +1 cm of water – expel 0.5 L of inspired air in 2-3 sec of respiration Figure 1. Contraction and expansion of the thoracic cage during expiration and inspiration, demonstrating diaphragmatic contraction, function of the C. Transpulmonary Pressure intercostal muscles, and elevation and depression of the rib cage. AP, - Difference between that in the alveolar pressure and Anteroposterior. pleural pressure - Measure of the elastic forces in the lungs that tend to II. MUSCLES OF VENTILATION collapse the lungs at each instant of respiration, called the recoil pressure - lungs can be expanded and contracted in two ways: 1. downward and upward movement of the diaphragm to lengthen or shorten the chest cavity Page 1 of 6 [PHYSIOLOGY] 1.10 MECHANICS OF RESPIRATION- Dr. Nicanor B. Lacuesta Jr. E. Surfactant and Surface Tension Principle of Surface Tension - When water forms a surface with air, the water molecules on the surface of the water have an especially strong attraction for one another – water surface is always attempting to contract - In the alveoli: water surface is also attempting to contract – expel air through the bronchi (try to collapse the alveoli) – elastic contractile force in the entire lung (surface tension elastic force) Surfactant - Surface active agent in the water - Produces by type II alveolar epithelial cells - DPPC (dipalmitoyl phosphatidylcholine) – partly dissolves in the water and the rest spreads over the surface Figure 2. Changes in lung volume, alveolar pressure, pleural pressure,and - Pure water= 72 dynes/cm transpulmonary pressure during normal breathing. - Fluid in alveoli but w/o surfactant= 50 dynes/cm - Fluid in alveoli but with normal amount of surfactant= D. Lung Compliance 5-30 dynes/cm - Extent to which the lungs will expand for each unit increase in transpulmonary pressure Occluded alveoli - Total compliance of both lungs together averages about - Positive pressure is produced in attempt to expel air 200 milliliters of air per 1 centimeter of water - Normal (with surfactant) – 4 cm of water transpulmonary pressure - Without surfactant – 18 cm of water - Pressure = (2x surface tension)/ diameter of the alveoli - Therefore, the surfactant is important in reducing the effort of respiratory muscles to expand the lungs - The lesser the diameter of the alveoli the greater the surface tension, the greater the respiratory effort – significant in premature babies F. Effect of the Thoracic Cage on Lung Extensibility - Compliance of the lung – thorax system is almost exactly 1⁄2 of the lungs alone - Combined system = 110 mL/cm - Lungs alone = 220 mL/cm - G. Work of Breathing Figure 3. Compliance diagram of the lung. Compliance diagram in a - Quiet breathing: muscles of respiration contract during healthy person. This diagram shows changes in lung volume during inspiration and passive relaxation during expiration changes in transpulmonary pressure (alveolar pressure minus pleural (elastic recoil) pressure). - 3 fractions of respiratory work: (1) To expand the lungs against the lung and chest - Characteristic is determined by elastic forces of the lungs: elastic forces, called compliance work or (1) Elastic forces of lung tissue – elastin and elastic work collagen fibers (2) To overcome the viscosity of the lung and (2) Elastic forces caused surface tension of the chest wall structures, called tissue resistance alveolar fluid and fluid lining other lung spaces work - The tissue of elastic forces tending to cause collapse of (3) To overcome airway resistance to movement the air-filled lung represent only about one third of the of air into the lungs, called airway resistance total lung elasticity, whereas the fluid air surface tension work forces in the alveoli represent about two thirds. - Energy required for respiration: - Quiet respiration: 3-5 % of the total energy expended by the body - Heavy exercise: increase in 50x of the original fraction of total energy expended - One of the limitations of the intensity of exercise is the ability of the person to provide energy for respiration IV. PULMONARY VOLUMES AND CAPACITIES - Spirometry – method for studying pulmonary ventilation Figure 4. Comparison of the compliance diagrams of saline-filled and air-filled lungs when the alveolar pressure is maintained at atmospheric pressure (0 cm H2O) and pleural pressure is changed to change the transpulmonary pressure. Page 2 of 6 [PHYSIOLOGY] 1.10 MECHANICS OF RESPIRATION- Dr. Nicanor B. Lacuesta Jr. lungs to their maximum extent and then expiring to the maximum extent ○ 4600 milliliters. The total lung capacity ○ equal to the vital capacity plus the residual volume ○ the maximum volume to which the lungs can be expanded with the greatest possible effort ○ about 5800 milliliters - All pulmonary volumes and capacities are about 20 to 25 per cent Figure 5. Sample illustration of Spirometer and how it works less in women than in men, and they are greater in large and athletic people than in small and asthenic people. A. Pulmonary Volumes - The tidal volume is the volume of air inspired or expired with each normal breath. (500 milliliters in the adult male) - The inspiratory reserve volume is the extra volume of air that can be inspired over and above the normal tidal volume when the person inspires with full force (3000 milliliters) - The expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after the end of a normal tidal expiration (1100 milliliters). - The residual volume is the volume of air remaining in the lungs after the most forceful expiration (1200 milliliters). Figure 7. Respiratory excursions during normal breathing and during maximal inspiration and maximal expiration Equations: Using the below equations, shows the interrelationships among pulmonary volumes and capacities. VC = IRV + VT + ERV VC = IC + ERV TLC = IC + FRC Figure 6. Average Pulmonary Volumes and Capacities for healthy young adult FRC = ERV + RV men and women B. Pulmonary Capacities Inspiratory capacity ○ equals the tidal volume plus the inspiratory reserve volume. ○ 3500 mL ○ amount of air, beginning at the normal expiratory level and distending the lungs to the maximum amount. The functional residual capacity ○ equals the expiratory reserve volume plus the residual volume. ○ 2300 milliliters ○ This is the amount of air that remains in the lungs at the end of normal expiration The vital capacity ○ equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume. ○ This is the maximum amount of air a person can expel from the lungs after first filling the Page 3 of 6 [PHYSIOLOGY] 1.10 MECHANICS OF RESPIRATION- Dr. Nicanor B. Lacuesta Jr. - Dead space air – part of the inspired air that does not reach the gas exchange area and fills up the conductive part of the respiratory system. - Normal dead space air = 150 mL in young male adult A. Anatomic vs Physiologic Dead Space - Anatomic Dead Space – air in the conductive part of the respiratory system - Physiologic Dead Space – air in alveoli with poor or absent circulation - Normal: Anatomic dead space = physiologic dead space - In diseased lung – physiologic dead space maybe 10x greater than anatomic dead space B. Rate of Alveolar Ventilation - One of the major factors determining the amount of oxygen in and CO2 in the alveoli - Equal to volume of new air entering the gas exchange areas times respiratory rate - VA = Freq x (VT – VD) - 12 x (500-150) = 4200 mL / min VI. FUNCTIONS OF THE RESPIRATORY PASSAGES A. Trachea, Bronchia, And Bronchioles - Airways kept open by cartilage rings and plates - Bronchioles (1.5 mm) kept open by transpulmonary pressure Resistance to airflow in the bronchial tree - Almost no resistance - Greatest resistance occurs in the larger bronchioles - In diseased lungs smaller bronchioles determine airway resistance due to - Muscle contraction - Edema in the walls - Mucus plugs Nervous and local control of the bronchial musculature - Weak sympathetic innervation due to few fibers penetrating to central portions of the lungs - Very much susceptible to norepinephrine and epinephrine released in the gland – stimulate β-adrenergic receptors to cause bronchial dilation or contraction Parasympathetic Constriction of the Bronchioles - Derived from the vagus nerve - Secretes acetylcholine – cause mild to moderate constriction Figure 8. Abbreviations and symbols for Pulmonary Function - Can also be activated from reflexes that originates from the lungs C. Minute Respiratory Volumes - Can be initiated by irritation of the epithelium - total amount of new air moved into the respiratory by noxious gases, smoke, or dust passages each minute - Can also be due to microemboli of small - equal to the tidal volume times the respiratory rate per pulmonary arteries minute - Normal = 500mL x 12 breaths per min = 6L/min Local Secretory Factors Often Cause Bronchiolar Constriction - Histamine and slow reactive substance of anaphylaxis – released by mast cells during allergic reactions V. ALVEOLAR VENTILATION - Smoke, dust, noxious gases can also cause non parasympathetic bronchoconstriction by acting on the lung tissue itself - Ultimate purpose of pulmonary respiration is to deliver oxygen rich air into the respiratory system (alveoli, alveolar sacs, alveolar ducts, B. Mucus Lining of the Respiratory Passageways, and Action of Cilia to and respiratory bronchioles) Clear the Passageways - Rate by which new air reaches respiratory segments - Mucus Layer – keeps epithelium moist and traps micro particles Page 4 of 6 [PHYSIOLOGY] 1.10 MECHANICS OF RESPIRATION- Dr. Nicanor B. Lacuesta Jr. - 200 cilia on each epithelial cell beats 10-20x per sec to clear this mucus layer into the pharynx C. Cough Reflex - triggered by irritation in the carina, larynx, bronchioles, and even the alveoli. - Afferent nerves pass through the vagus nerve to the medulla to trigger the following events: (1) 2.5L of air is rapidly inspired (2) Epiglottis and vocal folds forcefully shot (3) Abdominal muscles, and other muscles expiration contracts against the closed glottis to raise the pressure to 100 mm of Hg (4) Epiglottis and the vocal folds rapidly open and Figure 9. Anatomy of the Larynx air is explosively expired (70-100 miles per hour) - Airways collapse by the pressure, cartilage support invaginates and makes airways significantly narrower to bring out foreign noxious material. D. Sneeze Reflex - Similar to cough reflex – irritated nasal passages - Afferent nerve pass through the 5th cranial nerve to the medulla of the brain - Similar events occur but in the final stage the uvula is depressed and air is passed through the nose to clear out the foreign material. Figure 10. Laryngeal function in phonation, showing the positions of the vocal cords during different types of phonation. E. Normal Respiratory Functions of the Nose Articulation and Resonance Air conditioning functions - Organs of articulation (1) Air is warmed by the nose - 160 cm2 surface (1) Lips area of the turbinates and septum - rises to 1o (2) Tongue F of the body temperature (3) Soft Palate (2) Air is almost completely humidified – to within 2-3% of complete saturation - Resonators (3) Air is partially filtered (1) Mouth (2) Nose and Paranasal sinuses Filtration functions of the nose (3) Pharynx - Vibrissae – for larger particles - Turbulent precipitation – for smaller particles up to 6 micrometers. References: - Gravitational precipitation - for particles 1 to 5 Hall, J. E. (2016). Guyton and Hall Textbook of Medical Physiology (13th ed.). micrometers Philadelphia: Elsevier, Inc. - Lesser than 1 micrometer diffuse in the alveolar fluid and removed by alveolar macrophages - Lesser than 0.5 micrometer remain suspended VII. TEST YOUR KNOWLEDGE in the air and are expelled during respiration F. Vocalization 1. How much less are lung volumes and capacities of women compared to - Involves not only the respiratory system but also: males? (1) Speech control centers in the brain a. By 20-30% (2) Respiratory control centers in the brain b. By 10-15% (3) Resonance and articulation structures in the c. By 20-25% oral and nasal cavities d. By 20-30% - 2 Mechanical Functions: (1) Phonation 2. The minute respiratory volume is the product of the respiratory rate and (2) Articulation which lung volume? a. Inspiratory reserve volume b. Expiratory reserve volume Phonation c. Tidal volume d. Residual volume 3. What is the volume of dead space air normally found in healthy individuals? a. 100 cc b. 120 cc c. 150 cc d. 200 cc Page 5 of 6 [PHYSIOLOGY] 1.10 MECHANICS OF RESPIRATION- Dr. Nicanor B. Lacuesta Jr. 4. What is the average volume of the rate of alveolar ventilation? a. 4100 cc/min b. 4200 cc/min c. 1400 cc/min d. 1200 cc/min 5. What pressure keeps the smallest bronchioles (1.5 mm) open? a. Transpulmonary pressure b. Pleural pressure c. Alveolar pressure d. Recoil pressure 6. Afferent nerves pass through which cranial nerve in a cough reflex? a. CN V b. CN X c. CN XI d. CN XII 7. Afferent nerves pass through which nerve during a sneeze reflex? a. Trigeminal nerve b. Vagus nerve c. Accessory spinal nerve d. Glossopharyngeal nerve 8. Inhaled air is warmed by the nasal cavity by how much? a. By 1°F b. To within 1°F of body temperature c. to body temperature d. slightly above body temperature 9. Which of the following is not an organ of articulation? a. Lips b. Nose c. Tongue d. Soft palate 10.How much of the total body energy expenditure is dedicated to respiration? a. 1-3% b. 2-4% c. 4-5% d. 3-5% Answers: 1. C 2. C 3. C 4. B 5. A 6. B 7. A 8. B 9. B 10. D Page 6 of 6